Today, various techniques are used for mixing liquids that are stored in tanks, e.g. in process applications where a body of liquid requires equalization of differences in concentration and temperature, intensification of heat transfer, dissolution of a solid, dispersion of immiscible liquids or sparging of a gas.
The requirements are often different in different application areas. For example, in applications with beer fermenters or yeast tanks, mixing is typically applied for obtaining uniformity in concentration of ingredients and temperature. Within food, cosmetics and pharmaceutical industry, mixing of very exact and minute quantities of ingredients into relatively larger volumes of liquid is often performed. Within the pulp and paper, paint, petrochemical, plastics and mining industry, liquids with coarse particles are often mixed. The requirements for obtaining satisfactory mixing thus differ significantly and mixing is often performed by different types of rotary impellers or by liquid ejecting nozzles that are specifically designed for one application area. Baffles are often provided for preventing bulk rotation or swirling of liquid in a tank due to the effect of e.g. a rotating impeller or similar.
Generally, after a liquid has been mixed it is expelled from the tank in which it was mixed and the tank must be cleaned before a next mixing operation may commence. The cleaning should remove residues for a number of reasons such as for avoiding cross contamination, for avoiding build up of contamination layers and for preparing the cleaned tank for another batch of product. A liquid ejected for mixing the liquid content is often of the same type as the liquid content. A liquid ejected for cleaning the tank is generally a cleaning liquid, which gradually may be contaminated with the liquid that is cleaned off from the tank.
Cleaning is accomplished by a number of different arrangements. One such system, relating to cleaning only, is known from US 2009/0173362 A1. The document discloses a tank cleaning verification process. The process involves a spray head having a position, rotation angle and speed externally controllable and detectable from the outside of the tank.
However, in some cases the same arrangement is used for both mixing and cleaning. For example, patent document EP1324818 A1 discloses an arrangement with a jetting device adapted for introducing jets of liquid into a body of liquid inside a tank in order to cause stirring to the body of liquid. A jet nozzle is adapted for rotation about a first axis and about a second axis perpendicular, or non-perpendicular, to the first axis. Upon emptying the tank, the jetting device may serve for cleaning the tank by spraying liquid onto the tank walls.
Other techniques related to mixing or cleaning are described in patent documents U.S. Pat. Nos. 4,166,704 A and 5,620,250 A. US 2005/0207268 A1 relates to combined mixing and cleaning. One or more jets of liquid are introduced into a tank in order to cause agitation and stirring.
The techniques mentioned above are generally capable of mixing a liquid content of a tank (container), and to clean the tank after mixing is complete and the content is expelled.
However, the techniques suffer from an inability to efficiently perform mixing within a wide range of applications areas where different types of liquid contents are mixed, in particular if subsequent cleaning of a tank shall be effected with reasonable effort and/or if time and resources for mixing and cleaning should be kept as low as possible.